Re: [PATCH] perf_event_open.2: 4.9 PERF_EVENT_IOC_SET_DRV_CONFIGS support

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Hi Mathieu,

This feature seems not to have made it into 4.9. (Or did I 
miss something?) Is it still planned for a future release?

Cheers,

Michael

On 08/12/2016 07:56 PM, Mathieu Poirier wrote:
> On 12 August 2016 at 10:52, Vince Weaver <vince@xxxxxxxxxx> wrote:
>> On Thu, 11 Aug 2016, Mathieu Poirier wrote:
>>
>>> This manpage patch relates to the addition of the
>>> PERF_EVENT_IOC_SET_DRV_CONFIGS ioctl.
>>>
>>> link: http://www.spinics.net/lists/kernel/msg2318998.html
>>> Signed-off-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
>>> ---
>>>  man2/perf_event_open.2 | 6 ++++++
>>>  1 file changed, 6 insertions(+)
>>>
>>> diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
>>> index 3c894ccd1209..315b6a91079a 100644
>>> --- a/man2/perf_event_open.2
>>> +++ b/man2/perf_event_open.2
>>> @@ -2732,6 +2732,12 @@ The argument is a BPF program file descriptor that was created by
>>>  a previous
>>>  .BR bpf (2)
>>>  system call.
>>> +.TP
>>> +.BR PERF_EVENT_IOC_SET_DRV_CONFIGS " (since Linux 4.9)"
>>> +This makes it possible to pass configuration parameters to PMU drivers.
>>> +Configuration parameters are specific to each drivers.
>>> +
>>> +The argument is a pointer to the desired configuration parameters.
>>>  .SS Using prctl
>>>  A process can enable or disable all the event groups that are
>>>  attached to it using the
>>
>> This is a bit... vague.  So we're adding an interface to allow passing
>> arbitrary binary blobs through the perf_event interface?
>>
>> Is there any structure at all to these blobs?  From the other commit
>> messages it looked like you'd be passing in some sort of string.
> 
> I am adding an interface to pass PMU specific configuration to the
> driver.  Since PMU drivers exist for different architecture and
> drivers I am making the mechanism as generic as possible.
> 
> In this case the CoreSight Tracers need to know what "sink" to use for
> a trace session.  I've enhanced the perf cmd line tool to accept:
> 
> perf -e cs_etm/@sink=some_sink_definition/ ....
> 
> Everything falling with the '/' that is preceded by a '@' character is
> considered PMU driver material.  At this time the perf lexer accept
> two format:
> 
> "@cfg" and "@cfg=option".  The lexer will strip off the '@' and pass
> "cfg" and "cfg=option" to the kernel.
> 
> What gets sent down to the kernel is driver specific - it is up to the
> PMU drivers to parse and validate what's given to them.
> 
> This feature loosely mimics the filter enhancement where it is now
> possible to specify:
> 
> perf record -e some_event// --filter 'start 0xstart_addr,stop 0xstop_address' or
> perf record -e some_event// --filter 'filter 0xstart_address/offset'
> 
> Here it is up to the event to supply the mechanic to deal with the
> filter specification (I'm doing the same thing).  Keywords "start",
> "stop" and "filter" are common to both IntelPT and CoreSight tracers,
> making them ideal candidates for parsing in the core.
> 
> But for driver specific configuration "sink" is only applicable to
> CoreSight tracers...
> 
> Writing these lines I realise that "start", "stop" and "filter" are
> applicable to only two drivers (IntelPT and CoreSight).  Peter, do you
> think I should look for "sink" in the core parser, just like it is
> done for filters?
> 
> Guidance would be appreciated here.
> 
> Mathieu
> 
>>
>> Vince
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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